Project Summary/Abstract Within the Boston University School of Medicine (BUSM) Center for Biomedical Mass Spectrometry (CBMS), the BUSM MS Shared Instrumentation Laboratory (SIL) operates four mass spectrometers that are dedicated to meeting the increasing and complex needs of NIH- funded investigators. We propose to replace the 12-year-old LTQ-Orbitrap system in the BUSM SIL with a Thermo-Fisher Orbitrap Fusion Lumos Tribrid Quadrupole Dual Cell Linear Ion Trap Mass Spectrometer System, to significantly enhance performance and provide additional, critically important operating modes, to dramatically improve sensitivity and dynamic range and to gain the capability for obtaining very high resolution multimode/multistage data, and to increase system reliability. The system will deliver MS and multistage tandem MS measurements with narrow precursor ion selection width and high mass accuracy over a wide dynamic range. The Fusion Lumos will enable identifications and quantifications that are too challenging for presently available systems, and will generate novel fragments to facilitate structure elucidation of carbohydrates and glycoconjugates and detailed definition of post- translationally modified proteins and their interacting partners, to accelerate progress in ongoing projects related to human health. The requested system will improve the results that can be obtained by the BUSM SIL because structures will be able to be assigned to the biologically important compounds present in otherwise unresolved, unknown peaks; faster scan times and higher sensitivity will enable the identification of more components in complex mixtures and improve the reliability of the identifications; multistage dissociation modes will make available important and novel sequential fragmentation pathways to better define even fragile molecular structures, and the efficient transfer of high mass ions into the orbitrap will facilitate the study of large intact proteins and glycoproteins (e.g., antibodies), as well as covalent and noncovalent complexes. The research topics include cardiovascular and metabolic disease, diabetes, traumatic brain injury, Alzheimer disease, prion diseases, cancer, rheumatoid and Lyme arthritis, HIV/AIDS, infectious diseases, RNA binding proteins, and muscle regulation. Research projects of nineteen Major and seven Minor Users are described. Protocols that take strategic advantage of the advanced capabilities of the proposed system will be developed. Most investigators are located on the BUSM campus; the two external Users (both at HMS/MGH) collaborate with CBMS investigators.